Electron-coupled ultra high frequency coaxial transmitter



Oct. 25, 1960 J. E. HANDLER ELECTRON-COUPLED ULTRA HIGH FREQUENCY COAXIAL TRANSMITTER Filed May '7, 195'? 1 C m n Q m h v e a w 7 a m m 1 w 1W m l W M .i 2 2 Y w a a a 5 M 0 a w Y7 i 1 Hr v 5531 :i ll ii I as X. r 1 7 J 2 R W 1 y y o a i 9 w m w 2 W 9 1 a i Oct. 25, 1960 Q J HANDLER 2,958,050

ELECTRON-COUPLED ULTRA HIGH FREQUENCY COAXIAL TRANSMITTER Filed May 7, 1957 3 Sheets-Sheet 2 Oct. 25, 1960 J. E. HANDLER 2,958,050

ELECTRON-COUPLED ULTRA HIGH FREQUENCY COAXIAL TRANSMITTER Filed May 7, 1957 3 Sheets-Sheet 3 United States Patent ELECTRON-COUPLED ULTRA HIGH FREQUENCY COAXIAL TRANSMITTER Joseph E. Handler, Chicago, 111., assignor to Motorola, Inc., Chicago, Ill., a corporation of Illinois Filed May 7, 1957, Ser. No. 657,625

6 Claims. (Cl. 331-101) This invention relates to transmitters, and more particularly to ultra-high frequency coaxial transmitters for use in radar, radio, television, and the like. Coaxial transmitters have been used for generating very high frequency pulses or signals, such as used in radio beacon, television and other systems. In such transmitters there has been a long resonant output cavity with rather large shunt capacity between the output tube anode and ground, and in such structures it has been difficult to maintain good ultra high frequency characteristics, and to tune the same. The long cavities have made such transmitters larger and heavier than was desirable. There has also been a problem of enclosing all elements of the coaxial transmitter having dangerous voltages thereon, and shielding of the electromagnetic fields existing within the plate cavity also was imperfect. With previously known coaxial transmitters, it has been difiicult to replace associated vacuum tubes therein when needed, and introduction of modulating potentials on the anode was also somewhat complicated.

Accordingly, it is an object of the invention to provide a simple coaxial transmitter construction which is light weight and short in length.

Another object of the invention is to provide a coaxial transmitter for oscillating at a wide band of tunable frequencies and being tunable to any frequency within the band.

Still another object of the invention is to provide a coaxial transmitter in which all parts thereof at dangerous potentials are enclosed, and complete shielding of the electromagnetic field existing within the plate cavity is effected.

A further object of the invention is to provide a coaxial transmitter in which a vacuum tube may be readily inserted and removed and in which modulating potentials for the anode thereof may be simply introduced.

A still further object of the invention is to provide a coaxial transmitter which is effectively cooled by air.

One feature of the invention is the provision of a coaxial transmitter which is provided with an output resonant cavity terminated by a radial line so that the length of the output resonant cavity may be a small fraction of the length otherwise required therefor.

Another feature of the invention is the provision of a coaxial transmitter having an output cavity with a radial line connected to the tube anode which presents small shunt capacity which makes it possible to provide wide deviation with good modulation fidelity. This structure reduces sparking and corona at the anode.

A further feature of the invention is the provision of a coaxial cavity transmitter having a single adjustment mechanism for tuning the transmitter, and a single arijustable mechanism for controlling the power output of the transmitter.

A still further feature of the invention is the provision of a coaxial transmitter for radar applications including a central cylindrical cathode lead surrounded by a perforated cylindrical grid lead having connections designed ice to connect to the grid of a tetrode vacuum tube, a cylindrical screen lead coaxial with the grid cylinder and also provided with holes therein, and an output cavity having a cylinder which encloses an end portion of the screen cylinder and an end structure having an opening into which a tube may be projected to fit in engagement with the leads of the cathode, the grid and the screen in electrical contact with these elements. The output cavity end structure has an annular plate connected to the tube anode and positioned in the interior of the output cavity and separated by dielectric material from an end plate connected to the cylinder of the output cavity to form a radial line section. Air is supplied between the cathode cylinder and the grid cylinder and flows through holes therein into the output cavity from which it is exhausted through the tube so that the glass seals of the tube are kept cool during the operation thereof.

In the drawings:

Fig. l is a vertical section of a coaxial transmitter forming one embodiment of the invention and taken along line 11 of Fig. 3;

Fig. 2 is an end view of the transmitter shown in Fig. 1;

Fig. 3 is an end view of the transmitter shown in Fig. 1 showing the end opposite to that shown in Fig. 2;

Fig. 4 is an enlarged vertical section taken along line 44 of Fig. 3;

Fig. 5 is an enlarged vertical section taken along the line 5-'5 of Fig. 3; and

Fig. 6 is an enlarged vertical section of a portion of the transmitter shown in Fig. l.

The invention provides a high frequency coaxial transmitter for supporting a tetrode vacuum tube therein and being of minimum overall length. The transmitter includes a central coaxial line terminated with a filament plug and a cathode socket coaxial therewith for engaging filament and cathode terminals of a vacuum tube. A grid cylinder coaxial with the cathode cylinder has a socket at one end thereof for making electrical connection with a grid terminal portion of the vacuum tube which is internally connected to the grid of the vacuum tube. Surrounding the grid cylinder is a cylindrical sleeve which is shorter than the grid cylinder and has a socket for receiving the screen band of the vacuum tube. An electrically grounded cylinder encloses the grid cylinder and the screen sleeve to form a reentrant cavity which controls the oscillator frequency. An enlarged outer cylinder encloses one end of the grounded cylinder and is connected thereto at one end to form a resonant output cavity. The enlarged outer cylinder has an annular conducting plate forming the other end of the cavity, and the tube extends through the output cavity and into the cavities formed by the grid cylinder and screen sleeve. Inside the annular conducting plate, there is mounted an annular plate of dielectric material, and, on the inner face of the plate of dielectric material there is positioned a conducting anode plate having a socket in the central portion thereof engaging a wheel-like anode terminal of the tube. The outer annular conducting plate and the conducting anode plate, together with the dielectric plate therebetween, form a radial line which shorts the output cavity. The use of this radial line permits the output resonant cavity to be a small fraction of the wave length of the frequency of the resulting electron-coupled oscillator structure formed by the vacuum tube and the coaxial transmitter and thereby permits the overall length of the tube and transmitter to be much shorter than previously known devices. The grid and screen cylinders are perforated so that air may be drawn through the transmitter for cooling the same. Adjustable tuning capacity plates are provided in the reentrant cavity and the output cavity for controlling the frequency of the transmitter and'the output power respectively.

In Fig. 1, there is shown a coaxial transmitter adapted to receive a tetrode vacuum tube 11 of the well known lighthouse type to form an electron coupled oscillator. The tube 11 plugs into the transmitter 10, which includes an insulated filament or heater lead 12 extending from a suitable source of potential (not shown) and through a cathode cylinder 13. The filament lead 12 terminates with a spring-finger plug 16 and the cathode cylinder 13 terminates with a spring-finger socket 17 coaxial with the plug 16 and substantially larger than the plug 16. The plug 16 fits into a socket 18 in the vacuum tube 11 which is connected to the filament therein, and the socket 17 receives a cathode terminal connection 19 of the tube. These connections supply heater current to the tube and also make the required connection to the cathode of the vacuum tube. The lead 12 is fused to a pin 8 (Fig. 6) into which the plug 16 is threaded. The socket 17 is threaded over the end of a conductive connecting sleeve 9 connected electrically and mechanically to the cylinder 13. A glass insulating sleeve 7 is sintered to the pin 8 and the sleeve 9, and conducts heat from the pin 8 to the sleeve 9. The cylinder 13 is supported by an end cap 21.

Surrounding the cylinder 13 is a grid sleeve or cylinder 22 fitting into and sealed to an insulating spacer 23. The grid cylinder 22 is provided with holes 26 therein to permit flow of air therethrough and to also provide high frequency electron coupling therethrough. The cylinder 22 has at the upper end, as shown in Fig. 1, a socket 28 designed to engage a conductive terminal band 29 of the tube 11 which is connected to the control grid thereof.

A screen grid cylinder 31 is mounted on a ring 30 separating the cylinder 31 from the cylinder 22 and coaxially spacing these two elements. The cylinder 31 is provided with holes 32 therein to permit air flow and provide high frequency electron coupling and is surrounded by a spacer sleeve 33. The cylinder 31 is provided with an electro-conductive spring-fingered socket 35 for receiving a band-like terminal connection 36 of the tube 11 connected to the screen grid thereof. A screen terminal and feed-through 99 is connected electrically to the cylinder 31. An electrically grounded metal cylinder or housing 38 is positioned about the sleeve 33 and the washer-like spacer 23 and also supports the end cap 21. A pin 81 of nylon having a threaded portion 82 adjustably mounted in a tapped socket 83 in the cylinder 38 locks the elements 22, 30, 31, 33, and 38 together. The spacer sleeve 33 is provided with cooling and coupling holes 39 aligned with the cooling and coupling holes 32 in the cylinder 31, and the housing 38 also has cooling and coupling holes 40 aligned with the holes 39 and 32.

An annular plate 51 is brazed to the cylinder 38 and an outer cylinder 52 coaxial therewith. The cylinder 52 also supports conducting annular end plate 53 connected mechanically and electrically thereto by screws 54 threaded into lugs 55 riveted to the cylinder 52. Direct electrical contact is also provided between the plate 53 and the cylinder 52. A cup-shaped plate 61 of dielectric material is positioned between the plate 53 and an annular anode plate 64. The plate 64 has a flange 60 supporting a collet-like socket 65 for receiving a wheellike anode terminal connection 67 of the vacuum tube. Studs 66, of insulating material such as nylon, and shielding metal nuts 68 secure the plates 53, 61 and 64 together.

The plates 51, 53, 61 and 64 and the cylinders 52 and 38, form a resonant output cavity for the electron-coupled oscillator. The length of the cavity so formed is very much shorter than the length normally required for a resonant cavity of the frequency involved. This shortness in length is made possible by use of the radial line section formed by the plates 53, 61 and 64 with the consequent reduction in length and weight of the overall structure.

For tuning the output cavity an adjustment screw 71 having a plate 72 connected thereto is adjustably threaded in a nut 73 fixed to the cylinder 52. The screw 71 may be fixed in adjusted position by a set screw 74. The screw 71 may be turned in the nut 73 to adjust the position of the plate 72 relatively to a plate 77 connected electrically to the cylinder 38 to vary the capacitance therebetween and this is effective to adjust the power output of the oscillator. For tuning the reentrant oscillator cavity, a shaft 91 keyed to a bracket 92 on the cylinder 38, carries a shaped metal plate 93 forming a portion of a cylinder. The cylinder portion 93 may be adjusted farther into and out of the space between the grid cylinder 22 and the screen cylinder 38 to vary the capacity between the cylinders 22 and 38. By this adjustment of the plate 93 the oscillator may be tuned from one frequency to another.

An output terminal feed-through 96 (Fig. 4) is provided in plate 51 and includes a conductor 97 forming an output loop and connected electrically to the cylinder 38. A terminal feed-through (Fig. 5) mounted on the cylinder 52 is connected electrically to a spring contact 113 mounted on a dielectric block 112 on the interior of cylinder 52.

The spring contact 113 engages the anode plate 64 and applies plate voltage to the tube. A resistor 118 connected to the electrically grounded cylinder 38 is connected by connector 121 to the grid cylinder 22 to provide grid bias to the tube of the oscillator.

Cooling air is introduced into the transmitter through a tube 122 from a suitable source of air under slight pressure. The air is introduced through screened openings 125 in the end cap 21, and flows through the cylinder 22 over the cathode cylinder 13, and out through the holes 26, 32, 39, and 40 into the resonant output cavity, and cools all these elements. The air then fiows along the cylinder 52 and out through the contacts 65 engaging the anode terminal 67 of the tube 11.

The larger elements 13, 22, 31, 38, 51, 52, 53, 64, 92, and 93 all may be constructed of silver-plated aluminum so that they are very light in weight, and the entire transmitter weighs only about two pounds. Because of the radial section terminating the output cavity, the overall length of the transmitter 10 and the tube 11 is only about twelve inches. The spacers 23, 30, and 33 and the dielectric plate 61 must all be made of dielectric material having desired characteristics at the frequency involved, and polytetrafluoroethylene has been found to be suitable. The exterior of the cylinder 38 is electrically grounded for direct currents so that the plates 51 and 53, the cylinder 52, the cap 21 and the cathode cylinder 13 all are at direct current ground. The plate 64 is operated at a positive voltage, and suitable voltages are applied to the grid andscreen cylinders 22 and 31. The grounded exterior of the cylinders 38 and 52 shield the enclosed elements and prevent radiation from the transmitter.

The above described oscillator may be tuned through a wide frequency range with only adjustment of the shaft 91 through a 20% bandwidth. There is no mode-jumping, and excellent frequency stability is provided for any tuned condition. A model constructed in accordance with the invention operated excellently from 400 to 510 megacycles with an output up to 20 kilowatts. The power variation over this frequency band was only one decibel while the efiiciency obtained was about 85%. There is no arcing or corona at the anode of the tube. The shunt capacitance between anode and ground is only from l2-l5 micromicrofarads, which low shunt capacitance is due to the radial line section formed by the plates 53, '61, and 64. This low shunt capacity makes it possible to provide wide deviation with good fidelity. With the cooling system provided, only very low pressure air is q d to effectively cool the transmitter.

I claim:

1. In a coaxial transmitter device, the combination of an electron-coupled oscillator including a tube having a cathode, a grid, a screen and an anode, an elongated conductor adapted to be connected to said cathode, a grid cylinder extending along and surrounding said cathode conductor and coaxial therewith, a screen cylinder surrounding and extending along said grid cylinder, said grid and screen cylinders being adapted to be connected to said grid and screen of said tube respectively, said grid cylinder, said screen cylinder, and said cathode conductor forming a reetrant resonant cavity, a cylinder surrounding a portion of said screen cylinder, and a radial line connected across one end of said last named cylinder and forming an output resonant cavity, said radial line including a conducting plate connected to said anode of said tube.

2. In a coaxial transmitter device adapted to receive a tube having cathode, grid, screen and anode electrodes and to form an electron-coupled oscillator circuit therewith, the combination of an elongated cathode, conductor, a grid cylinder extending along, coaxial with, and surrounding said cathode conductor, a screen cylinder surrounding and extending along said grid cylinder, an electrically grounded cylinder extending along and surrounding said screen cylinder, said cathode conductor, said grid cylinder, said screen cylinder and said grounded cylinder forming an input resonant cavity for controlling the frequency of the oscillator, said cylinders having openings near one end thereof, a fourth cylinder surrounding the portion of said grounded cylinder having openings therein, and a radial line terminating said fourth cylinder to form a resonant output cavity, said radial line including a conducting plate connected to said anode of said tube.

3. In a coaxial transmitter device including a tube having an anode and a plurality of other electrodes connected in an electron-coupled oscillator circuit, the combination including, a coaxial structure connected to said other electrodes of the tube and forming a reentrant cavity which controls the tuning of the oscillator, said structure including an outer grounded conducting cylinder, an annular conducting plate mounted about said grounded cylinder, an outer cylinder mounted at one end thereof on said plate, a second annular conducting plate connected to said outer cylinder at the other end thereof, a third annular plate of dielectric material mounted on the inner face of said second plate, and a fourth annular conducting plate in engagement with said third annular plate, said second, third, and fourth plates forming a radial line which shorts the resonant cavity formed by said outer cylinder, said fourth plate having connectors at the inner diameter thereof for connection to the anode of the tube of the transmitter device.

4. In a coaxial transmitter device including a tube connected in an electron-coupled oscillator circuit, the combination including an elongated cathode connector, a conducting grid cylinder extending along, coaxial with and surrounding said cathode connector, a conducting screen cylinder surrounding and extending along an end portion of said grid cylinder, an electrically grounded conducting cylinder extending along and surrounding said screen cylinder and being substantially coextensive with said cathode conductor and said grid cylinder, said cathode connector and said cylinders forming a reentrant cavity which controls the tuning of the oscillator, an annular conducting plate mounted about said grounded cylinder intermediate the ends thereof, an outer cylinder mounted at one end thereof on said plate, a second annular conducting plate connected to and closing the other end of said outer cylinder, a third annular plate of dielectric material mounted on the inner face of said second plate, a fourth annular conducting plate in engagement with said third annular plate, said second, third, and fourth plates forming a radial line which shorts the resonant cavity formed by said outer cylinder, said fourth plate having connectors at the inner diameter thereof for connection to the anode of the tube of the transmitter device, and means insulated from said outer cylinder for making an electrical connection through said outer cylinder to said fourth plate.

5. In a coaxial transmitter device, the combination of an electron-coupled oscillator including a tube having a cathode, a grid, a screen, and an anode, reentrant cavity means connected to said cathode, said grid, and said screen of said tube to provide oscillation-s therein, said reentrantcavity including coaxial cylinders with the outer cylinder being held at ground potential, and an output cavity connected to said anode and having a. cylinder surrounding a portion of said reentrant cavity and electrically connected to said outer cylinder thereof, said output cavity including a radial line connected across one end of said cylinder thereof, said radial line including first and second conducting plates with an insulating plate therebetween, said first conducting plate being connected to said cylinder of said output cavity and said second conducting plate being connected to said anode of said tube for applying oscillations from said tube to said output cavity, the entire outer surface of said transmitter device including said outer cylinder of said reentrant cavity and said cylinder of said output cavity being at ground potential for direct current.

6. In an electron-coupled oscillator, the combination of a vacuum tube having cathode, grid, screen and anode electrodes, reentrant resonant cavity means coupled to said cathode, grid and screen electrodes of said tube for providing oscillations in said tube, and an output resonant cavity surrounding a portion of said reentrant resonant cavity, said output resonant cavity including a radial line section forming one end thereof, said radial line section having a pair of annular conducting plates 'with an annular dielectric member positioned therebetween, one of said plates being connected to the anode of said tube for applying oscillations therefrom to said output cavity through electron coupling in said tube, said dielectric member being constructed to have low shunt capacitance to provide wide band operation.

References Cited in the file of this patent UNITED STATES PATENTS Reinsma July 117, 1956 Andrews Aug. 20, 1957 OTHER REFERENCES 

